The circulating neutrophil has three major tasks that it must accomplish before it can carry out its final task of phagocytosis. First, it must deform and flow through the capillaries often while in a stimulated state. Second, it must recognize sites of inflammation in the post-capillary venules and rapidly attach to these sites by rolling and then firmly adhering to the endothelial cells that line the walls of these venules. Finally, it must migrate through the vessel wall and into the surrounding tissue by a continuous process of adhesion and detachment. The fundamental mechanical processes that underlie each of these tasks are not well understood and, thus, our future plans will focus on three basic studies designed to elucidate these mechanical processes. First we plan to study the deformation and flow of neutrophils into capillaries when the cells have been stimulated by a specific chemoattractant or cytokine or priming agent, either separately or together. The mechanical sensitivity of our experimental system will allow us to study low levels of these stimulating agents when no obvious morphological changes have occurred. Secondly we plan to study adhesion and detachment of the unstimulated and stimulated neutrophil from artificial surfaces and from endothelial cells and other neutrophils. Again, the mechanical sensitivity of our system will allow us to approach this study from the most fundamental level by first determining the forces and lifetimes of individual chemical bonds. Larger bond forces from multiple bonds will be the sum of the basic canonical forces sustained by the single bonds. Finally we plan to characterize the pressures, contraction forces and rates of the fundamental polymerization and depolymerization processes that are responsible for the motion of the cell. In all cases the emphasis is on the underlying mechanical characteristics that govern the life of the neutrophil. Only by understanding these fundamental mechanical processes in vitro can we explain the cell's complex behavior in vivo. The work is significant in that it is a fundamental mechanical study of the inflammatory response. We will determine how neutrophils stiffen when stimulated by cytokines and chemoattractants because the activation of neutrophils causes a significant increase in resistance to their flow, and thus to blood flow, through the microcirculation, especially the capillaries. We will measure the fundamental bond forces and bond lifetimes between neutrophil receptors and their ligands, which will tell us what forces are involved in the rolling and sticking of neutrophils to the endothelial cells of the circulation. Finally, we will measure the forces and polymerization rates for neutrophils when they activate and crawl.